BEIRUT — The Syrian military used airstrikes and heavy artillery to assault rebel-held areas of the central city of Homs on Saturday, residents and anti-government activists said, as the government renewed efforts to retake that perennially restive and divided city.

A new government push in Homs has been expected since the Syrian army, backed by the Lebanese militant group Hezbollah, took over the nearby border town of Qusair this month after it was held by rebels for about a year.

The new fighting suggested that President Bashar Assad was continuing his push to consolidate control of areas stretching from the capital, Damascus, and up the country’s western spine along the Lebanese border to Syria’s Mediterranean coast, the president’s ancestral homeland and a bastion of his supporters.

Homs has existed as a divided city throughout much of the two-year uprising, with some neighborhoods under rebel control. The government’s bombardment of the Baba Amr neighborhood in early 2012 was one of the first assaults to herald the escalation of the state’s use of heavy weapons against residential areas harboring rebels; the government has periodically retaken some areas, sometimes losing them again months later.

Fighting raged in several areas of the city, including the historic city center and around the Khalid bin al-Waleed mosque, and explosions sent columns of smoke rising skyward, according to residents and video posted by activists.

Dr. Walid Fares, an activist in Hamidiyeh, an area of the Old City in Homs, said the government had spent several days mobilizing troops around surrounded rebel areas in Homs, then pummeled some areas with airstrikes.

Then, he said, “they used rocket launchers for hours.” He said government troops “shelled us with heavy mortar shells” and “raided us from four different directions.”

Fares said that electricity and telecommunications in the old city had long been blocked or damaged, and that he relied on satellite connections. As he talked, explosions echoed in the distance.

“They’ve blocked everything here, electricity, phones, water,” he said. “The only thing they haven’t blocked is the air we breathe.”

The government’s news agencies said the army was making progress against “armed terrorist gangs” in Homs.

The opposition Syrian National Coalition issued an appeal for international powers to help the rebels and said the government offensive “threatens the unity of Syria” by reinforcing the possibility that supporters of Assad could create a rump state.

Supporters of Assad in Syria and elsewhere have said that is not his goal, and that he seeks to maintain a united Syria.